Profile measurement of moving metal strip

ABSTRACT

For measuring the transverse thickness profile of metal strip advancing longitudinally, e.g., from a rolling mill, the strip is scanned along a line across its path by thickness measuring means using an X-ray beam at an acute angle to the strip plane, while the thickness is simultaneously measured at a selected point of the line by means having an X-ray beam at a like but opposite angle, the two measuring means being carried by C-shaped structures with mutually staggered arms accommodating the beams at crossing angles whereby the scanning means can pass the other means without mutual interference of function. By combining the signals from the two measurements, longitudinal thickness variations during scanning time are in effect eliminated and an accurate, rapid determination of transverse profile is obtained. The operation is especially useful in relation in hot rolling of strip, permitting adjustments during rolling, automatically if desired, to correct or avoid profile errors, with particular advantage in avoidance of such distortions of shape as may occur, upon rewinding an ultimate cold rolled strip, because of nonflatness of profile that cannot be corrected in cold rolling.

ilnited States Patent [191 Sivilotti et a1.

[ PROFILE MEASUREMENT OF MOVING METAL STRIP [75] Inventors: Olivo G.Sivilotti; William Elfyn Davies, both of Kingston, Ontario, Canada [73]Assignee: Alcan Research and Development Limited, Montreal, Quebec,Canada [22] Filed: Nov. 3, 1971 [21] Appl. No: 195,339

[52] US. Cl 250/833 D [51] Int. Cl. G011! 23/02 [58] Field of Search250/833 D [56] References Cited UNITED STATES PATENTS 3,179,800 4/1965McNamara 250/833 D X 3,474,668 10/1969 Mangan 250/833 D X 3,531,82710/1970 Dragonette 250/833 D X Primary Examiner-Archie R. BorcheltAtt0rneyRobert S. Dunham et a1.

35 ail/ i s .L, l I CONTROLLED l x- RAY B T.? J

- TRANSV. AND LONGIT.

P ROFI LE LONGH.

PRO FILE 7,; o I F FE R E N c2 CIRCUIT J 5 T R A N s v, P R o F! 1. E

SCAN THICKNESS Dl FFER EN CES FROM CENTER THICKNESS [5 7] ABSTRACT Formeasuring the transverse thickness profile of metal strip advancinglongitudinally, e.g., from a rolling mill, the strip is scanned along aline across its path by thickness measuring means using an X-ray beam atan acute angle to the strip plane, while the thickness is simultaneouslymeasured at a selected point of the line by means having an X-ray beamat a like but opposite angle, the two measuring means being carried byC-shaped structures with mutually staggered arms accommodating the beamsat crossing angles whereby the scanning means can pass the other meanswithout mutual interference of function. By combining the signals fromthe two measurements, longitudinal thickness variations during scanningtime are in effect eliminated and an accurate, rapid determination oftransverse profile is obtained. The operation is especially useful inrelation in hot rolling of strip, permitting adjustments during rolling,automatically if desired, to correct or avoid profile errors, withparticular advantage in avoidance of such distortions of shape as mayoccur, upon rewinding an ultimate cold rolled strip, because ofnon-flatness of profile that cannot be corrected in cold rolling.

34 Claims, 9 Drawing Figures THl'CKN ESS PROFILE WIDTH 8' TIME [4 ore116, i973 PAIENIEUnm 15 1973 SHEET 2 BF 6 PAHNIEUBBI 16 ms SHEET 30F 6SCAN Posmorv AND DIRECTION READiNG PATENIEnncI 16 1915 3.766386 7 SHEETa UF 6 PATENIEDUEI 16 I973 3.766.386

aa f zz /4 w I E L CONTROLLED: I X-RAY I VOLTAGE J THICKNESS PROFILETRANSV. I I M TL? 75 AND Loreen.

PROFILE o l WIDTH 2, TIME Y- I 74 l LONCHT. I A

I PROFILE m L? L 78 TIME 'DIFFERENQE 83 CIRCUIT l TFTK. 1? 506 TRANSV.64 I PROFLE w 9 SCAN THICKNESS Di FFEREN CES FROM CENTER THICKNESSPROFILE MEASUREMENT OF MOVING METAL STRIP BACKGROUND OF THE INVENTIONThis invention relates to procedure and apparatus for measuring thethickness profile across a moving strip, expecially a rapidly movingstrip of sheet metal as delivered, for example from the work rolls of arolling mill, to be rewound on a conventional take-up reel or mandrelunder appropriate tension.

Investigations leading or related to the present invention have revealedthat a high degree of thickness uniformity crosswise of a rolled strip,for example of aluminum (including aluminum alloys), and indeed of othermetal as well, is extremely desirable, not only to achieve highdimensional precision for such products but also to satisfy handling andmarketing requirements in respect to proper rewinding and especially foravoidance of off-flatness or other serious defect, e.g., as may resultfrom excessive local areas of stress in the interlapstress distributionin rewound coils.

Thus if the cross-section of the strip isnon-uniform, e.g., in thatthere are appreciable differences in thickness across the strip betweenits lateral edges, unequal stresses may be imposed at various localitiesin successive laps of the coil as or after the strip is wound undertension, with localized concentrations that can in at least many casesexceed the yield strength of the metal. For example, at a number oflocalities along a longitudinal band of excessive thickness there may beactual deformation of the metal, exhibited as local waves or the likewhich are seen when the strip is removed from the coil and whichrepresent, in effect, localized extensions of the sheet relative toother parts of it. Studies have now shown, as indicated above, that suchproblems of severe off-flatness or other defects in the tinished productmay arise from cross-sectional, i.e., profile errors, and of course, thelatter may in themselves represent an undesired departure fromdimensional requirements where close tolerances are needed.

Although it appears that for a given metal, such as aluminum and itsalloys, products of softer metal are most affected by non-uniformprofile because the tolerance for stress concentration is dependent onthe maximum stress that the metal .cansupport without yieldingplastically, problems of the above sort may exist to some degree in mostrolled products, i.e.,- strip that is this tolerance could be eventighter depending on the alloy and the recoiling temperature.

Accordingly, it has been found that it would be very desirable to obtaina measurement of the strip thickness profile during actual processing ofthe strip, e.g., as the strip is being delivered from the rolls of amill, whether single or tandem, which may be effectively adjusted orcontrolled to maintain desired profile characteristics. Under suchcircumstances, the operator can keep the mill (which may be an early onein a sequence of hot and cold rolling) adjusted to provide desiredflatness characteristics, especially as to uniform thickness and can infact do so while the mill is processing the strip. Thus for example, ifat the very outset of a rolling pass the profile can be broughtto'proper condition and if frequent measurements are then rapidlyavailable, corrective adjustments of the mill, as to roll bendingforces, coolant distribution or the like, can be brought about beforeany detected departures from desired profile reach an unsafe or unwantedvalue.

So far as could be ascertained during investigation leading to thepresent invention, available profile gauges that are supposedly capableof measuring the thickness profile of a moving strip do not providesuitably rapid or accurate results for satisfactory control of stripproperties during rolling. One such device has embodied a traversingthickness gauge of the X-ray type, which scans the thickness of thestrip across its width, by moving perpendicularly to the path of striptravel. It is known, however, that the overall thickness of the stripvaries during a rolling pass, essentially apart from the profilecharacteristics or changes in them. lnthe meter just described, effortto account for these longitudinal thickness variations has been directedto averaging such variations over long lengths of the strip. This meansthat the speed of response is relatively slow, in that a significantprofile reading is only obtainable after a relatively long time, and mayinvolve many hundreds of feet or thousands of feet of strip, or even amajor part of an entire pass. In consequence, while the defect in themill adjustment may become known for control of a subsequent pass, orperhaps a remainder of the pass under test, large quantities of strip ofunsatisfactory contour may have been rolled and may have to be scrapped.v

The longitudinal thickness variations are so designated because they arechanges which are observable from place to place along the length of thestrip (as it passes) and which are deemed to affect the thickness of thestrip in the same way at all points or zones across it. In simplifiedterms of examples, these longitudinal thickness changes can be caused bychanges in the vertical height of gap at the roll bite, while trueprofile changes can be caused by changes in roll contour, e.g., inregions of roll crown or concavity. Thus if a longitudinal thicknesschange occurs while a traversing gauge is measuring profile, the profiledetermination will be inaccurate unless suitable correction is made forthe longitudinal variation. v

Another available system for profile examination has involved atraversing X-ray gauge which has associated with it a stationary X-raygauge at an adjacent position in the path of the delivered strip. Thereadingsof these meters are connected for suitable combination of theirsignals, as in a difference circuit, whereby'long term longitudinalgauge variations are cancelled out; It has been found, however, thatrolling operations also commonly involve longitudinal gauge variationsof a short term character, which in the rolling of aluminum may' betypically of the order of 2 percent over a distance equal to onecircumference of the back-up rolls (typically 15 feet) in a 4-high mill,and which can be responsible for faulty profile error signals greaterthan 0.2 percent. That is to say, even in the short distance of passagebetween the scanning meter and the stationary meter, there can besufficient gauge variation-to provide an erroneous profile measurement,approaching or equal to the above mentioned tolerance within which stripprofile should be maintained.

It will be understood that changes in the profile configuration or shapeare usually relatively slow, whereas these so-called longitudinal gaugevariations may be quite rapid, affecting the entire width of the strip,without altering profile shape. Thus as indicated, the best equipmentthat is understood to be presently available fails to take into accountthese short term longitudinal variations in sufficient manner to avoidprofile measurement errors of significant value, at least if it isdesired to obtain rapid or essentially instantaneous readings asdistinguished from readings which involve averaging of one sort oranother over a protracted interval. Accordingly, there is need formethods and apparatus that will provide strip profile measurement in aprompt and effective manner, and more specifically, for such methodsand/or apparatus of rugged, reliable and highly accurate character,representing improvement in these or other respects of convenience andsimplicity over what has been available or may otherwise have beenproposed heretofore.

SUMMARY OF THE INVENTION To the foregoing and other ends and indeed tothe underlying aim of affording improved profile measurement across amoving strip, the invention is generally predicated on the provision ofmethods and apparatus whereby the moving strip is scanned for thicknessmeasurement crosswise thereof along a predetermined line transverse ofthe strip path while simultaneously a thickness measurement is effectedat a selected point substantially onthe line of scanning, with thicknessmeasuring beams or the like which are mutually arranged to traverse thestrip, as at an angle to each other, so that there is no mutualinterference between the simultaneous thickness-sensing operations.Signals representative of the thickness values from the two operationsare suitably combined, as by difference, to yield a scanned reading ofthe transverse thickness profile wherein longitudinal thicknessvariations'are effectively cancelled out. a

More specifically, it has been discovered that effective thicknessreadings and essentially simultaneous modification to eliminate, so tospeak, thickness variations lengthwise of the strip, can be obtained bycrossing beams of thickness-sensing function, e.g., beams traversing thestrip at acute angles which extend in opposite directions relative tothe path of the strip, so that one beam may be maintained at a singlepoint in the.

path while the other scans across the path along a line passing saidpoint, without the thickness-sensing function of either beam beinginterrupted or affected because of or by the other.

A particularly important aspect of the invention resides in theapparatus, which constitutes a profile gauge appropriate for fast-movingstrip delivered froma rolling mill, wherein two pairs of supportingmembers are provided, the members of each pair being respectivelydisposed near opposite faces of the strip and being arranged so that athickness-sensing beam, e.g., of X-rays or other penetrating radiation,traverses the strip from one member of the pair to beam-receiving meansin the other member of the same pair. Each pair of members isadvantageously arranged so that the members are in effect disposed inseries along the strip path, e. g., one member upstream and the othermember downstream of a desired line of scan perpendicular across thepath, the members of the pairs being oppositely disposed in the latterrespect so that considering the strip as between both pairs, each pairhas one of its members directly above a member of the other pair. Thismutually interfitting relation of the pairs of members permits bothmembers of each to be disposed close to the scanning line and permitsfree movement of one pair relative to the other, while maintaining theabove relation, during the desired scanning.

Cooperating with this arrangement the thicknesssensing means, includingthe beam generating and projecting device, is arranged in each pair sothat the beam is projected obliquely from one member to the other, e.g.,at an acute angle to the strip surface, and the projection paths of thebeams are thus disposed at a substantial angle to each other. At leastone of the pairs of members is arranged to be movable across the strippath, for thickness scanning, while the other is advantageously used ata fixed location, for example at the center of the strip path, and byvirtue of the mutual crossing nature of the beams, there is nointerruption or interference of sensing operation as the movable pair ofmembers scans past the other pair.

A presently preferred and particularly advantageous arrangement of theapparatus embraces a structure joining the members of each pair at alocality outside the edge of the passing strip, so as to constitute thepairs as C-shaped structures respectively embracing the strip path, or apart of it, from opposite sides, thereby affording a very rigid, stablesupport for each thickness-measuring means whether used in one positionor moved in scanning function across the path of the strip.

With operation of the sort described, it is found that a highly accuratedetermination of the transverse thickness profile can be achieved,essentially independent of even the short-term longitudinal variationsof thickness that commonly occur in the rolling of strip. It may beexplained at this point, that even though such longitudinal variationsmay be sufficiently small to keep the strip thickness within a fairlynarrow gauge tolerance, i.e., ordinarily meeting gauge specificationsfor the product, the difficulties of improper profile are occasioned bythickness differences (crosswise of the sheet) which can well be withinsuch limits of gauge tolerance. In other words even though the overallgauge variations may seem slight, circumstances may be such that theireffect on profile determination, if not cancelled out, is objectionablyserious.

Furthermore, as explained hereinbelow, correction of profile faults may,in many cases be best achieved, or indeed only achieved, during hotrolling operations and this well ahead of cold rolling procedure. Undersuch circumstances thickness or gauge may vary more than slightly duringthe rolling operation with which profile measurement is associated,either because highly precise gauge control is not ordinarily requiredat such stage or because it may be impossible to achieve under selectedconditions of hot rolling. In any event, experience has indicated thatover-all gauge variations, whatever their rnagnitude, are a likelihoodin rolling operations, sufficient even in short lengths to affect theaccuracy of profile sensing across a rapidly moving strip.

With the present procedure, and particularly utilizing the novel profilemesuring apparatus, it has been found possible to achieve very rapid,indeed essentially instantaneous and reliable determinations ofthickness profile, which can be displayed on an oscilloscope or as achart tracing or otherwise, or which indeed can constitute data or betranslated into data appropriate for control of the mill through whichthe material is being processed. Particularly in that the longitudinalgauge variations, as measured by the stationary X-ray beam or the like,are found to be characteristic of the entire width of the strip, whilethe profile remains essentially unchanged over relatively long lengthsof the material, the invention affords effective cancellation of thelongitudinal thickness variations and yields a satisfactorily accuraterepresentation of profile. The two preferably continuously producedmeasurements are at each instant effected on the same transverse regionof the strip, i.e., at points which passed through the roll bite at thesame time, it having now been discovered that essentially only in thismanner can there be assurance of eliminating the effect of underlying,longitudinal, thickness changes which can occur sufficiently rapidly asto impair the accuracy of profile readings quite seriously even when itis attempted to make them at rather closely spaced localities, i.e., onebeyond another, in the path of strip travel. 1

Thus the operator of the mill can be kept informed at frequentintervals, indeed essentially continuously if desired, regarding thecharacter of departures of the product from desired profile, and he cantake steps promptly, by appropriate adjustment of mill operation insuitable, known manner, to correct such errors, indeed in advance oftheir becoming so great as to impair the acceptability of the ultimateproduct.

A further, specific aspect of the invention involves procedure andapparatus whereby profile readings of the moving strip are converted tosuitable control signals which are in turn employed for automaticcontrol of the rolling mill itself, so that corrections of strip profilecan be achieved as necessary and advantageously in such manner thatactual departures from desired uniformity across the strip are minimizedand kept withinv a suitable tolerance. In one effective embodiment,profile departures across the strip are employed for control ofconventional coolant supply to the rolls of the hot mill, whereby rollcontourv is maintained forachieving desired uniformity of profile of thehot-rolled strip product. 1

Other significant features of the apparatus include means mounting bothof the supporting structures to be moved transversely of the strip path,as by roller ele-. ments coacting with appropriate tracks beneath thepath, preferably also with suitable driving means to advance thescanning structure so that. its thicknesssensing device may .traversethe entire width of the strip, with appropriate return drive. Forinitial set-up of a pass through the mill, the two structures can bemoved entirely to opposite-sides of the strip path, and then thestationary thickness-sensing members can be replaced in desiredposition, for example at the center. line of the strip, and can be keptthere throughout operation, while the other structure ismoved across thestrip to perform the scanning function.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified perspectiveview of one of the two coacting X-ray thickness measuring units orgauges. embodying the invention (by way of example), this unit A beingfor continuous thickness response at a single longitudinal locality.

' paratust.

FIG. 2 is a like simplified view of the second unit or gauge,specifically unit B for traversing the moving strip to sense thicknessat regions across the same.

FIG. 3 is a further, similar view showing units A and B in functionalrelationship to each other and a passing strip, the units being hereillustrated as seen each from the opposite direction to the views ofFIGS. 1 and 2.

FIG. 4 is a side elevational view of one representative unit, e.g., unitB as seen in FIG. 2, with certain further parts in phantom or diagram.

FIGS. 5 and 6 are opposite end views of a representative unit, forexample unit B as seen respectively from the left-hand and right-handends of FIG. 4.

FIG. 7 is a simplified and diagrammatic view, in longitudinal elevationand in vertical section (as at-the right-hand strip edge in FIG. 3),showing the passage of a strip through the coacting gauge units A and Bfrom a rolling mill to the rewind coil.

FIG. 8 is a simplified diagram illustrating the conversion of signalsfromunits A and B, by combination, for attainment of true profilemeasurement.

FIG. 9 is a schematic view of one example of a system for controllingmill roll configuration in response to strip profile determinations.

DETAILED DESCRIPTION Referring first chiefly to FIGS. 1 to 7 of thedrawings, the illustrated example of the apparatus involves twotransversely movable X-ray gauge units A and B, which are basicallyembodied in a conventional C-frame structure for metal strip thicknessmeasurement, but with ari unusual alteration of such structure inaccor-, dance with the invention. The units are arranged to inspect(FIG. 7) a metal strip 14 delivered from the work rollsl 16 of a rollingmillstand and rewound under tension as a coil 17 on a suitably drivenmandrel or core 18,-thelstrip 14 being preferably kept level by passageover a guide roll 19. Although in a general sense the inventio i isconceived applicable to any mode of thickness m %:1surement wherein abeam of penetrating radiation hether X-ray, nuclear or other), isprojected throug the metal strip and is there modified in accordance iththickness, unusual advantages and convenience are attainable with X-raygauging techniques, i.e., when employed as inthe illustrated example ofap- Unit 'A (FIGS. 1 and 3 which may be employed for detectinglongitudinal thickness variations, comprises a lower frame arm 20projecting horizontally from a vertical gSUPPOI't structure 21, and anupper horizontal v positioning of the substantially coextensive'arms20,22 includes thickness mea'suring'means'arranged to project asensitive beam, e.g., of X-rays, angularly through the strip passageregion, between the endsof the arms as indicated at 23. Specifically,the beam generating and projecting means may be embodied in theoutertween the upper and'lower arms (see FIG. 3) so that the thin X-ray beam23 traverses the moving strip for attenuation of the received intensityof radiation by absorption, in accordance with strip thickness, as usualin X-ray gauging.

For movement of the unit crosswise of the strip path, there are a pairof forward rollers or wheels 26 beneath opposite sides of the outer end24 of the arm 20, and a pair of rear rollers or wheels 27 beneathopposite sides of the vertical support 21. The wheels 27 are much morewidely separated than the wheels 26, inasmuch as the support structure21 is of approximately double width relative to the arms, for rigidinterconnection of the latter in their staggered position. Thus,considered as a carriage, the unit is in effect relatively very wise atthe rear region 21, with the consequent advantage of special stabilityand rigidity.

Preferably the forward wheels 26 are carried by a gimbal arrangementcomprising a sub-frame 28 pivoted on a horizontal axle 29 that issupported from the outer end 24 of the arm 20, so that the truckconsisting of the sub-frame 28 and the wheels 26 can rock about an axisthat extends parallel to the arm and to the path of movement of theunit, i.e., crosswise of the strip. See also the further illustration oflike means on unit B, described below. Hence, in effect the unit has athreepoint support, being the two rear wheels 27 and the front wheeltruck 28-26, to avoid twisting forces or other rocking or torsionalstresses being transmitted to the C-frame.

The complemental unit B, shown in FIGS. 2 to 7 as contemplated forscanning entirely across the strip path, is exactly similar inconstruction to unit A, except that the lower and upper arms 30, 32 ofunit B may be very substantially longer, i.e., in projecting from thevertical support or column 31-, to accommodate the scanning operation,whereas unit A may only have to be moved from a position clear of thestrip at one side, to a locality where the elements 24, 25 arenear thecenter of the strip. With unit B, thickness is sensed by a thin X-raybeam 33 passing through the strip at an acute angle equal but oppositeto the angle of the beam 23. Means for generating and projecting thebeam 33 may be situated in the outer end portion 34 of the arm 30, andthe beam is received and its intensity sensed by suitable means .in thehead 35 of the arm 32. The as- I sembly is supported by rear wheels 37,below the column 31, and forward wheels 36 carriedon a gimbal frame 38rocking on an axle 39, all identical in structure and function to thesimilarly numbered parts 26 to 29 of unit A. I

Although. the vertical support and arms of each unit can be made ofother beam or truss arrangements, the units are advantageouslyfabricated as box-like parts of heavy (e.g., one-half inch) steel platepieces rigidly secured together (as by welding except where internalaccess may be needed), all in a manner similar to certain presentlyknown C-frame X-ray gauges, this welded plate box construction beingillustrated at arms 20 and 22 in FIG. 7. Internally the units, for usewith hot rolling, may enclose suitable cooling means (not shown) forcirculation of water or other coolant in appropriate portions of thehorizontal arms and upright supports or columns, with flexible hoseconnections as may be required.

As indicated above, suitable X-ray beam projecting and receiving meansare situated in the structure parts 24, 25 and 34, 35. Such means arewell known in the art, as well as related instrumentation and circuitry,and details are therefore unnecessary here; indeed under known X-raythickness gauging technology, reliable systems capable of measuringsmall, rapid variations are available, embracing means whereby thereduction in detected X-ray intensity due to absorption in the strip, ina generally exponential relation to thickness, is translatedelectronically to an electrical signal representative of actualthickness. Such instrumentalities, including devices producing highlyintense, accurately aligned X-ray beams and sensitive detection devices,with low-noise reading and translating circuits, are applicable to thepresent invention wherein the beam is directed through the strip at anacute angle rather than perpendicularly, and corresponding specificdescription or illustration of such known technology is omitted, e.g.,in FIGS. 8 and 9. For completeness, however, the angularly disposedX-ray tubes and detecting devices,.the latter being embodied asphotomultiplier tubes, are schematically indicated in FIG. 8, e.g., theX-ray generators 40 and 41 in elements 24 and 34 and detectors 42 and 43in elements 25 and 35, correspondingly related to units A and B.

As shown in FIGS. 1-5, 7 and 8, the upper surface of the arms 20, 30, isconveniently beveled at 44,45, in a plane perpendicular to the X-raypath 23 or 33, and an appropriate window 46 or 47 is mounted in thecorresponding beveled surface, of conventional character transparent toX-rays, to allow passage of the related beam in usual manner, similarwindows (not shown) being employed for beam ingress at the underside ofthe elements 25 and 35. As will also be understood, adjunctsconventional in X-ray gauging can be included if desired, such asremotely controllable magazine (not shown), in each of the structures24, 34, of metal thickness standards insertable into the beam inposition parallel to the strip path, for calibration of the system whenstrip is not present.

The Units A and B move crosswise of .the path of the metal strip 14 on aplurality of rigidly supported, parallel rails, 50, 51 and 52. As'shown,the widely spaced rear wheels 27, 27 and 37, 37 travel on the outerrails 50, 52, and likewise, respectively, the outside wheels of theforward pairs 26, 36. The inner wheels of the latter pairs ride on thecentral rail 51. Although other lateral guidance can be provided, theunit carriages also conveniently include guide rollers rotatable onvertical axes and disposed below the units so as to bear on verticalfaces of the rails 50, 51 and 52. Thus, for example, as seen in FIGS. 4,5 and 6 relative tounit B, a pair of such guide rollers 54 is associatedwith the gimbal frame 38 at the forward endof the arm 30, and a similarpair of such rollers 55, is associated with the column 31 at thelocality of the rear wheels 37, identical guide rollers being similarlyprovided for unit A. Accurate tracking of the units is thus achievedwithout using flanges on the bearing wheels 26, 27, 36, 37, as mightpossibly allow the wheels to ride up or derail.

Each of the units is advantageously provided with power-driven means fordisplacing it along the rails, such means being particularly importantfor the scanning carriage, unit B, but being also desirable for unit Afor convenience of moving the latter into and out of its centraldetecting position. Such mechanical drive, for each unit, can be of anysuitable form, and for purposes of illustration is schematically shownwith unit B in FIG. 4, as including a reversible drive motor 57 coupledto turn a sprocket wheel 58 that is arranged, as for example withcooperating guide sprockets 59, 60, to advance the carriage along aroller chain 62 which extends below the carriage, in a crosswisedirection relative to the metal strip path. Thus the chain 62, fixed atits ends 63, 64 in suitable abutments, not shown, is guided between thewheels 59, 60 and over the drive wheel 58, for positive drive of thecarriage in either selected direction. Electrical connections, includingpower lines for the motor and for the X-ray tube, control or likeconductors, and likewise conductors for delivering the thicknesssignals, may extend into and from the unit in a large flexible cable 65extending below the carriage to appropriate terminal means, not shown.

The critically significant feature of the illustrated units with theirstaggered and interfitting arm members, is that the respectivethickness-sensing X-ray beams 23, 33 extend at an angle to each other aswell as each at an acute angle to the vertical, or more particulary,that the beams in effect cross at a'single line in the plane of thestrip path, i.e., a line which extends perpendicularly across the strip14, as best seen in FIGS. 3, 7 and 8. In this manner, simultaneousthickness sensing is attainable by both units, always with respect totwo points in the rolled strip which had passed the roll bite together.In consequence as explained above, the effect of longitudinal thicknessvariations can be eliminated, yielding rapid and truly accurate profilemeasurements.

For such purpose, a preferred mode of operation is as follows: as orafter the strip is initially moved past the locality of the units to besecured for winding on the reel 18, unit A-is brought from a retractedposition clear of the strip, very preferably to a locality as indicatedin FIG. 3, where its X-ray beam 23 traverses a central point of thestrip path, it being understood, however, that useful function of thisbeam can be achieved at some other fixed locality of the path. For

each profile reading, e.g., after continuous delivery and coiling of thestrip-has begun, the other unit B, from a position entirely clear of thepath at the other side, is advanced across the path so that its beam 33scans entirely across the strip, from one side edge to the other, alonga line which intersects the locality of the beam 23. In each suchforward or reverse scan a continuous reading, or set of successive,closely spaced readings, can thus be obtained for the relative thicknessvalues across the strip at positions longitudinally displaced because ofthe strip movement, while at the same time longitudinal variations instrip thickness are sensed continuously or at identically closeintervals by the beam 23 of unit A. All of this is achieved without mechanical or other interference between the gauge carriages of the unitsor their sensing X-ray beams. 1

The apparatus preferably includes means signalling the successivepositions of unit B as it scans across the metal strip and also meanssignalling the beginning and end of such scan, particularly incooperation with means for reversing the drive so that if desired, theunit can automatically travel back-and forth, in continuous or periodicsuccession of scanning operations. Inasmuch as means for-generatingsignals of such functions may assume various forms, as ofmechanical,electrical or optical nature, and indeed the scan reverse or scandirection signals may be readily obtained with limit switches or withdevices photoelectrically actuated on passing the edges of the strip,specific details of such instrumentalities or devices of inherentlyconventional character are omitted, and FIG. 4 schematically shows, forsimplified illustration, combined means 68 for all these purposes. Thus,for like simplicity of example, means 68 is shown as responsive to theposition of the unit relative to the chain 62, through suitable means,including a line 69 from a device 70 controlled by a chain-connectedelement such as the idler wheel 60, suitably adjusted in terminalresponses for actual position of edges of the strip 14 relative to thechain. Instrumentalities such as means 68 or other devicesof'appropriate structure and nature can consist of individually wellknown elements for these functions, and can thus provide scan-reversesignals, e.g., in a line 71, for controlling the motor- 57 to drive theunit successively back and forth, and related scan direction signals inline '72 representing the direction, i.e., forward or reverse, in whichthe unit is about to move or is moving, and canalso provide signals, asin line 73, which denote the position of the X-ray beam 33, e.g., itsinstantaneous distance from a selected strip edge regardlesss ofdirection gauges, specifically from the detecting means 42, 43,

are interfaced or otherwise directed to appropriate amplifying andtranslating means 75 and 76 respectively. The means 75, being responsiveto the signals of the scanning unit B, establish a varying signal orseries of signals which represent changing thickness but necessarilyinclude thickness variations occurring both crosswise of the strip andlengthwise thereof, the. longitudi-' nal variations,being thuscharacterized by change with time,being here desired to be eliminated.The signals developed through the means 76, from the stationarythickness sensing unit A, represent longitudinal profile changes only,i.e., changes occurring with time and thus corresponding to that part ofthe readings of device 75 which is occasioned by suchlongitudinalvariations.

Thus conveniently signals from devices 75 and 76 are supplied to asuitable difference circuit 78 whereby in effect the longitudinal orsolely time-varying signals are subtracted from the total, time. andwidthvarying profile signals and thus afford in the correspondinglycontrolled device 80 an indication or other registration or read-out ofthe true transverseprofile, with the ion gitudinal or time variationseliminated or balanced out ashas been explained above. v

Simplified graphic presentation of one" instance of these relationshipsis shown in the plots at the righthand side of FIG. 8, wherein thethickness readings,

greatly exaggerated, are represented by the vertical axis and thefactors of width (i.e., crosswise position) and/or time are representedby-the horizontal axis. Thus the profile curve 81 represents the type ofprofile reading which could be obtained from the means 75, wherein eachpoint across the curve has a-valueaffected not only by transversethickness differences but also by longitudinal variations. v

The curve 82 is intended to represent changes of lo'ngitudinal thicknessduring the time of scan, i.e., the thickness changes which occur, at theselected point,

with the longitudinal travel of the strip during the scanning time.Finally, the curve 83 shows the true transverse profile as determined bythe means 80, translating the operation of the circuit 78 and thuseliminating the longitudinal variations by mathematically appropriatesubtraction. Hence the plot 80 shows the true crosswise contour, forexample as related to a suitable base line 84, which may represent theactual thickness of the strip at the center and may now be considered asa straight line, i.e., unaffected by longitudinal variations. Hence oneconvenient type of output signal, as at 85, from the means 80 forreadout in an X-Y chart recorder, oscilloscope or the like may be thescanned thickness differences (positive, negative or zero), across thestrip, from the thickness of the strip at its center.

It may be explained that although the curves 8 82 and 83 are drawn as iffrom a single instance, they nevertheless illustrate the kind ofresponse that is obtainable with the described procedure and apparatus;most particularly, the curves show that if as may often occur, there isa significant longitudinal variation (curve 82) this can soaffect thesimple scanning determination (curve 81) as to distort it veryundesirably from the true profile reading, such as in curve 83. It mayalso be noted that in actual readings with instrumentation of the sortcontemplated, the mechanically or electronically plotted curves may notbe perfectly smooth (as here shown for simplicity) but may becharacterized by minute vertical variations of instrumental or otherorigin. Nevertheless the results are'basically of the nature hereillustrated, demonstrating the important function of the invention inproviding essentially instantaneous, highly accurate profile readings.

it is conveniently sufficient that the profile be signalled or plottedas thickness departures from a straight line, as if the strip had onetruly plane surface, and likewise simply as relative differences inthickness from point to point across the strip, although theinstrumentation may, if desired, yield actual thickness values, e.g., asvertical cross-section dimensions taken at a single transverse lineperpendicular to the strip edges. Information derived from relativevariations, e.g., as in plot 83 of FIG..8, is ordinarily adequate forpurposes of mill control or adjustment to achieve desired profileflatness tolerance in the rolled strip.

In practical embodiments of the apparatus, dimen sional relationshipscan be as required .for accommodating the desired strip path and forproviding high rigidity and stability of the sensing units. The angulardirection of each X-ray beam is correlated with the structure of theunits, and asindicated, the employment of the angularly crossing beamspermits close juxtaposition of the units for reading on substantiallythe same transverse line, while affording room for units of ample sizeto achieve the above mentioned rigidity and stability. A presentlypreferred angle for each of the beams 23 and 33 is 24, measured from thevertical or normal to the passing strip surface. To a considerableextent, the larger this angle, the greater the likelihood'of unwanted.error in the resulting readings due to casual or incidental movementsof the units, e.g., rocking, vibration, or other unavoidabledisplacement. For practical purposes, it is presently believed thatangles up to about 45 might still permit some utility of result withapparatus of the nature shown. Conceivably with appropriate design ofthe equipment smaller angles, say

down to 15, may be employed, but the selected angle of 24 or thereaboutis now thought to represent a feasible optimum.

By way of specific example of the procedure, a typical use involvesrapidly repeated profile-measuring scans back and forth across aluminumstrip 60 inches wide and one-eighth inch thick emerging from the finalstand of a tandem hot mill, i.e., the rolls 15, 16 of such stand (FIG.7), at a speed of 1,000 feet per minute, such hot mill strip beingcoiled or wound at 17 under suitable tension. A useful scanning speedfor the unit B across the strip may be 10 feet per minute, representinga single scan interval, in one direction for the 60 inch strip, of about30 seconds. As will be appreciated, much slower scanning speeds can beemployed if desired, or conceivably faster speeds if electronicinstrumentalities are appropriately designed for handling such signals.In the illustrated example, each scan can be recorded on a pen-type, X-Yrecorder chart, or alternatively presented on an oscilloscope that ispreferably accompanied by memory means for subsequent readback ifdesired.

In one instance of design of units A and B, each of the upright orsupporting sections 21 or 31 may have a horizontal dimension in thedirection of strip travel, e.g., between wheels 27 or 37, of about 30inches, and a height such that with the arms of each unit dimensionedproportionally in the general manner shown, the vertical gap between theparts 24, 25 or 34, 35 is about 14 inches. For the unit A, intended tosense the thickness along the center of the strip, the arms may projectso that the distance or throat dimension between the strip-adjacentvertical wall of the upright 21 and the X-ray beam 23 is about 60inches; the corresponding distance in the scanning unit B may be aboutinches. The equipment as described or as suitably modified to suit therequirements of a given mill and size of rolled strip, can-be applied toprofile measurement on a large variety of such materials, e.g.,aluminum, steel, brass and various other metals, which may for examplerange in strip width from 20.inches to inches andstrip thickness from0.030 inch to 0.250 inch. The procedure is appropriate for any of alarge range of strip speeds, e.g., from to 3,000 feet per minute, itssuitability in that respect being a special advantage in contrast toprevious modes of profile measurement.

As indicated above, the invention, althoughusefully applicable forprofile determination of any travelling sheet material (includingmeasurement on cold rolled sheet strip for inspection purposes) is of,special'utility in the examination of hot rolled strip asdirectlydelivered by a hot mill, whether at the end of hot rolling or even at anintermediate stage in a seriesvof hot rolled passes. As explained above,strip profile errors which most commonly arise and are most troublesomein hot rolling or as a result thereof, are difficult to correct insubsequent cold rolling; indeed it is generally recognized, underrolling theory, that the profile of strip which has been hot rolled andis supplied to a cold-mill should not be expected to be capable ofsignificant change in shape in a cold rolling operation.

As also explained above, profile errors of the hot rolled strip havebeen found to represent a cause of offflatness or other shapedeterioration in an ultimate, re-

wound, cold rolled sheet product/Particularly in the final stripflatness, as distinguished from profile considered alone, is found to bebadly affected by profile errors. This loss of flatness is understood tobe due largely to local concentration of rewind stresses in the coil,notably when the thick regions of successive turns are drawn tightlyagainst each other. Indeed it can be shown mathematically, taking therewind tension and the values of yield strength and Youngs modulus forthe metal, that relatively small errors of thickness, i,e., in profile,can result in distortion of the corresponding thick regions of the stripon coiling, especially where the excessive thickness is in a relativelysmall proportion of the strip width. Thus in the case of a number ofcommon aluminum alloys, and where the rewind tension may be only percentof the yield strength, there will be localized stretch, and distortionsuch as waviness or the like when the strip is later uncoiled, if thereare one or more thick longitudinal bands (often at the edges, orsometimes elsewhere) totaling less than 10 percent of thecross-sectional area. I

The problem is more pronounced in softer alloys, having low yieldstrength, but rewind tension may have to be quite large in other cases,e.g., steel, thereby increasing the possibility of flatness. Moreover,the stress concentration and resulting elongation tend to increase fromthe inside diameter of the coil to the outside, and serious defects ofshape, due to uneven stretch, may arise even when theoreticallyunlikely. In consequence of all the foregoing it is extremely importantto determine and control the profile of the material during hot rolling,especially so as to avoid serious profile errors that in effect survivecold rolling.

As also indicated above, the actual thicknesses across the width are notthe primary matter of concern, but the question is one of relativedifferences. Indeed troublesome thickness variations across the stripmay ordinarily be smaller (by an order of magnitude factor of l/ 10)than the longitudinal thickness variations, e'.g., even than thelongitudinal variations which are within normal gauge tolerance for hotrolled products. These circumstances emphasize the importance ofsimultaneously sensing both types of thickness variation throughout eachprofile-measuring scan, in the manner afforded by the invention.

Imporatnt uses of rapid and frequent profile readings on the stripdelivered by the hot mill are not only to ascertain the suitability ofthe strip for cold-rolling, but most particularly to enable the operatorto adjust the mill for avoidance or correction of undesired profile,indeed at times when the departure from intended contour is stillinsufficient to affect the ultimate product. Suitable correctivemeasures may involve change of collant to the rolls of the mill atselected zones across each roll, or modification of bending forces onthe rolls by change of force in suitable bending jacks, or adjustment ofscrewdown forces as to affect roll bending generally or for example tocorrect unbalance, orother shape-controlling alteration of the operationof handling and rolling the strip. In many cases, the procedure ofmaking corrective adjustments is effectively performed in a manualfashion, as by the attention to and manipulation of necessary controlsby the operator in response to observation of the displayed profileplots or measurements.

It is also -a feature of the invention to utilize the Sig nals from theprofile measuring equipment to effectuate automatic control of therolling mill, e.g., involving adjustment of one or more means related tothe shape or contour of the rolled strip, in such fashion as to maintainsubstantially uniform profile of desired character, across the strip. Asan example, one effective I mode of automaticcontrol especially whererapid changes in roll gap shape due to rolling load variations may beinconsequential or may be corrected by other means, can involveadjustment of the coolant liquid to the rolls of the mill, e.g., as maybe delivered at a multiplicity of zones across each roll, by spray orstreams from suitably positioned outlets, in known manner. With suchcontrol of the coolant, which may be water, oil, or other liquidespecially suited for the purpose, the temperature of each roll isaltered in localized fashion, and correspondingly the local shape ordiameter of the roll, such thermal adjustment being well known forcorrecting roll contour errors, whether occurring thermally or even bysome wear, and for correspondingly determining the profile of the metalbeing rolled.

Although any of a variety of known electronic or similar systems can beutilized for translating thickness signals, e.g., from the outputcircuit 85 of the profiledetermining means of FIG. 8, into roll zonecooling changes, FIG. 9 schematically shows, for example, one suitablecontrol system for this purpose. This system provides individual controlof coolant flow at a multiplicity of zones of the rolls, e.g., includingoperations of opening a valve in each coolant flow line or leaving suchvalve open, when a decrease of thickness appears at the particularcorresponding zone of thestrip, or shutting off the flow or keeping itclosed, when the thickness increases at the particular zone. To theextent that other or additional roll contour or pass gap contouradjustments are preferable or indicated in a particular case, it will beunderstood that appropriate means may be utilized or added as necessaryunder like-control of the profile signals.

The system of FIG. 9 is thus specifically designed to receive the trueprofile signals derived from successive forward and reverse scanningoperations ofunit B and the continuous readings'of unit A and toconvertthese signals into control of valves in the coolant linesto therespective zones of the mill. Although other means can be employed forsuch conversion, a convenient arrangement is to compare each seriesofthickness, readings, of a given scan, with an average taken from thereadings for the previous scan, thereby determining changes from .thelatter, whereupon the roll coolant flow is controlled in response tosuch changes. Assuming that the mill has been initially adjusted or isspecially adjusted early in the run to deliver strip of proper profile,this system is effective and sensitive to small changes, in a mannersufficient to maintain proper profile by correcting profile errorsbefore they reach sufficient magnitude to affect the delivered stripadversely.

In particular, the illustrated system receives the following signals:(a) profile signals as in the output circuit or line of FIG. 8,representing values, during scan across the strip, of differences ofthickness (which may be positive, zero or negative) from the thicknessat the center or other point selected for measuring longitudinalvariations; (b) scan position signals, as in line 73 from FIG. 4, whichmay, for example, be a voltage or like quantity representing in value,the instantaneous distance from'one selected edge of the strip in thedirection toward the other; and (c) a signal, as derived in line 72 ofFIG. 4, representing the direction of scan,

being significantly effective at the beginning of each scan, or at thechange of scan direction.

The scan direction signals in line 72 control a correspondingtwo-position relay 90 whereby when or as a forward scan is initiated therelay contact assembly 91 is raised so that profile signals from theline 85 are routed by branch line 92 and line 93 to anaveragedetermining and memory unit 95 of suitable character whichresponds to the lowest and highest values of the thickness signals andtemporarily stores the thus computed high-low average as representing anaverage thickness signal for the forward scan. When or as the scanningunit reverses direction as represented by a new signal in line 72, therelay 90 drops its assembly 91 and a circuit consisting of the lines 92and 96 directs the thickness signals of the reverse scan (from line 85)to another average-determining and memory unit 97, identical with theunit 95 and functioning to compute the average of the highest and lowestthickness readings and temporarily store such high-low averageof thereverse scan in an appropriate memory circuit.

During each scan, thickness signals at 85 are also directed via line 98to a computing converting unit 100, which also receives from a line 101the stored reading of the average thickness value from the immediatelypreceding scan. Specifically, when the direction relay 90 has itscontacts 91 in the upper position for the forward scan and the unit 95is determining the average value for the forward scan and the forwardscan profile signals are being delivered to the converting unit 100, theunit 100 is simultaneously connected through lines 101 and 103 toreceive the stored average thickness value of the previous, reverse scanunit 97. When the relay contact assembly 91 is in its lower position,i.e., during the immediately following, reverse scan, the unit 100(which continues to receive profile signals, now of the reverse scan, inline 98) is connected to receive the stored average thickness of theprevious, forward scan through lines 101 and 105. Hence the unit 100 hasan input which consists of the thickness difference signals during theoccuring scan whether forward or reverse, and simultaneously thetemporarily stored average thickness signal from the immediatelypreceding scan, i.e., reverse or forward. It will be understood thateach of the elements 95 and 97 includes appropriate reset provision, forexample under suitable control of the relay element 90, whereby thetemporarily stored average signal is in effect erased just before thebeginning of the next scan in which that element must compute anaverage.

The unit 100 includes suitable electronic instrumentalities forcomparing the received thickness-difference readings with the computedaverage from the preceding scan, and for delivering, in its outputcircuit 107, successive signals, which may be of digital nature ifdesired, that represent departure (if any) of each instantaneouszone-localized signal from such preceding average value. The deliveredsignal may conveniently be one which is positive for increase ofthickness or negative for decrease of thickness, or zero for no changein thickness, e.g., no change exceeding a suitable threshold.Simultaneously the scan position signal received in the line 73 isdelivered to a position selection instrumentality 108, which has a setof outputs 110-1, 110-2, 110-3 to and including 110-N, equal in number(N) to the roll coolant zones of the controlled mill, as for exampletwenty such zones. The function of the device 108 is to convert theposition values to discrete zone indicia and thus to provide a controlor triggering signal, successively in the output lines 110-1 to 110-N,in accordance with the position of the scanning device (unit B)crosswise of the strip, this being an absolute positional selection,regardless of the direction of the scan.

The system also includes a corresponding number of electronic gatesystems generally designated 112 and identified as 6-1, 6-2, G-3 to G-Ninclusive, which are respectively controlled by the output lines 110-1to 110-N of the position selection unit 108, and which respectivelycontrol a like series of switches, as for example suitable powertransistor switches designated 114 and individually identified as PT-l,PT-2, PT-S through PT-N. The latter switches correspondingly control aseries of solenoid valves 116, being valves S-l, 8-2, 8-3 through S-N inthe coolant flow lines generally designated 118 to the roll coolantzones schematically shown at 120 relative to the rolls 15, 16 of thecontrolled mill, there being a total number N of such lines and of suchzones. As will be apparent, the converted profile signals from thedevice (representing departures from the previous scan) are alsosupplied to the gate systems 112, for the line' 107 through a manifoldcircuit consisting of lines 124-1, 124-2, 124-3 through 124-N, to theunits G-l, 6-2, 6-3 through G-N.

It will now be understood thatthe gate systems 112 and the switches 114are appropriately designed, with suitable electronic circuits, so that agiven solenoid valve 116 is only subjected to a control signal if thecorresponding gate system simultaneously receives a triggering signalfrom the scan position selector 108 and a positive or negative signalfrom the thickness signal converter 100. More particularly, although theconverted thickness signals are continuously available to all the gatesystems, the latter can only function, i.e., in succession, when thecorresponding triggering signals are received from the selector 108through'the appropriate lines -1 to 110-N. I

Thus as the given scan (for example a forward scan) progresses, at eachzone a triggering signal is delivered to the corresponding gate systemof such zone while such gate system is then in fact receiving theconverted thickness signal (from unit 108) appropriate to such zone. Ifthe thickness signal is positive, the corresponding power transistorswitch 114 is actuated, relative to the associated solenoid valve 116,e.g., to open the valve if the latter has been closed or to leave thevalve open if it has been open. On the other hand, if at the time agiven gate system receives itstriggering signal from the selector 108,the-converted thickness signal is negative, the corresponding transistorswitch 114 then closes the related solenoid valve 116 or keeps it closedif it has been previously set in closed position. Should the convertedsignal from the device 100 be a zero signal, there is no effect on thecorresponding gate system when the related position signal is receivedand there is no change in the related transistor switch or solenoidvalve, the latter simply remaining in its previously set position,whether closed or open.

The described system of FIG. 9 affords an essentially continuous controlof roll coolant flow at the several zones of the mill, depending on theprofile readings in each successive scan, in a manner appropriate toprevent profile errors from growing to a significant value.

Coolant flow is turned on or off or left unchanged in effeet inaccordance with the instructions of the profile reading in each scan,conveniently compared with the average of the immediately precedingscan, so that the shape of the roll is maintained, by thermal control oflocal expansion and contraction, in a suitable manner to correctdepartures of profile from desired condition and in effect to maintainthe desired overall characteristics of strip profile. As will beunderstood, the electronic instrumentalities employed in the severaldevices schematically indicated as units in FIG. 9, e.g., for performingthe various described functions, may be of conventional nature; suitablemeans and circuits for such individual operations are indeed well knownand therefore require no detail description here.

Although the system is manifestly capable of further refinement in anymanner that circumstances may require, it is-presently conceived thatthe described conversion of signals and control of coolant valves isadequate for maintaining roll shape in many cases. For instance, whilethe scan averaging can with suitable, complex electronic circuits bedetermined from a reading of all zones or positions in a given forwardor reverse scan, simplicity of circuitry'is achieved with provision fora high-low average alone, and such is deemed to be adequate under usualcircumstances as where substantial changes in profile occur at no morethan a slow or moderate rate.

For convenience, the system is illustrated as controlling coolant flowto a single roll stand, which may indeed be sufficient; alternativelythe coolant flow can be simultaneously controlled to the rolls 'of allstands of a tandem mill. Likewise the coolant-controlled stand or standsmay involve various roll arrangements whether of the simple two-rollform shown or of four-high character. Of course, the profile signals canbe employed for other types of corrective control, such as work rollbending means, or in very wide mills, backup roll bending means,'insubstitution for-or in supplement to the described coolant control. Itwill be understood that all installations of the invention for automaticcontrol may preferably also include means providing visual indication orrecord of the measured profile, as contemplated in FIG. 8, whereby theoperator may take additional corrective steps, even replacement of badlyworn rolls, if need for same becomes evident.

The invention is in all of these ways well suited to attain its objects,especially for determining the transverse profile of travelling metalstrip in a rapid and immediately useful manner, with good accuracy andwithout significant error caused by longitudinal thickness variationsthat may occur during a profile-measuring scan. 7

It is to be understood that the invention is not limited to the specificinstrumentalities and operations herein set forth by way of illustrationbut may be carried out in other ways without departure from its spirit.

We claim:

1. A method of measuring the thickness profile across alengthwise-moving metalv strip, comprising:

a. scanning the strip along a line transverse of the direction ofmovement, with a first thicknesssensitive beam, to provide signalsrepresenting thickness valuesat the succesively scanned striplocalities; v

b. simultaneously throughout said scanning step measuring the thicknessof the moving strip at a selected stationary point, substantially withinsaid line of scanning, with a second thickness-sensitive beam to providesignals representing variationsin thickness of the strip at said pointduring the scanning step; said beams being mutually disposed andarranged so that as the first beam scans past said selected point eachbeam is transmitted through the strip and received, forthickness-measuring operation, without interference with thethickness-measuring operation of the other beam at said point; theaforesaid disposition of the beams including respectively directing themalong paths at sufficient, oppositely extending angles to theperpendicular to the strip surface, to prevent interference of saidthickness-measuring operations; and d. combining the signals that resultfrom the first and second beams to provide a transverse profiledetermination which is substantially unaffected by longitudinal vstripthickness variations as represented by thickness variation signals fromthe selected point.

2. A method as defined in claim 1 in which each of said angles is atleast about 15.

3. A method as defined in claim 2 in which each of said angles is about24.

4. A method as defined in clain 1 wherein: beamgenerating beam-sensinge. said first and second beams are transmitted through the strip betweencorresponding pairs of cam-generating and beam -sensing elementsrespectively near opposite faces of the strip,

f. the elements of the pairs being oppositely staggered in positionlengthwise of the strip, and said beams being correspondinglytransmitted at oppositely inclined acute angles to the strip,

g. said scanning step including moving said pair'of elements for thefirst beam past the said pair of elements for the second beam. a

5. A method as defined in claim 1, in combination with producing saidmoving strip'by rolling operation which is adjustable for altering theprofile of the pro duced strip, said strip being in movement lengthwisefrom said rolling operation, which includes 7 h. detecting departure ofthe transverse profile of the aforesaid determination from a desiredprofile, and

i. adjusting the rolling operation in accordance with said detecteddeparture to' correct the profile of further production of said strip.6. In a method of measuring the thickness profile across a length-wisemoving metal strip, the steps coma prising:

a. scanning the strip along a line perpendicular to the direction ofmovement, with a first X-ray beam which traverses the strip at anacuteangle to'the surface thereof and which isreceivedafter saidtransver'sal, to provide signals representing thickness valuesat thesuccessively scanned strip localities; and v v i b. simultaneouslythroughout said scanning step directing to the strip, at a selectedpoint substantially within'said line of scanning, a second X-ray beamwhich traverses the strip at an acute angle to the surface thereof andwhich is received after said traversal,to provide signals representingvariations in thickness of the strip at said point during the scanningstep; p j

is c. the aforesaid traversal angles of the beams being mutuallydisposed to provide a sufficient angle between beams as the first scanspast the second at said point to prevent interference between saidthickness-sensing operations with the beams.

7. A method as defined in claim 6 in which each of the beams is directedto the strip at an angle between about 15 and about 45 to theperpendicular to the strip surface, and the angle between the beams isat least about 30.

8. A method as defined in claim 6, which includes combining the signalsfrom the first and second steps by diminishing the thickness values ofthe first step signals in accordance with thickness values ofsimultaneous second step signals for cancelling the thickness variationsat said point from the transverse measurements to provide adetermination of transverse thickness profile of the strip which issubstantially independent of longitudinal thickness variations.

9. A method as defined in claim 8, in which each of the beams isdirected to the strip at an angle between about 15 and about 30 to theperpendicular to the strip surface, and the angle between the beams isat least about 30.

10. A method as defined in claim 9 wherein d. each of said X-raytraversing and signal-providing steps is effected by projecting thecorresponding X-ray beam from a first element near, one face of thestrip and receiving and sensing such beam at a second element near theopposite face of the strip, said elements for the first beam beingseparated longitudinally of the strip on selected opposite sides of saidscanning line, said scanning operation being effected by moving saidelements for the first beam together across the path of the strip, and

f. said elements for the second beam being separated longitudinally ofthe strip on opposite sides of the scanning line which are respectivelydifferent from the aforesaid selected sides, whereby said second beamelements are disposed clear the scanning movement of the first beamelements.

11. A method as defined in claim 8, in combination with producing saidmoving strip by rolling operation which is adjustable for altering theprofile of the produced strip, said moving strip being in its aforesaidlongitudinal movement as delivered under tension from saidrolling'operation, which includes g. making successive determinations oftransverse thickness profile along a continuous strip by the aforesaidsteps,

h. detecting unwanted thickness values in such profile in saidsuccessive determinations, and

i. adjusting the rolling operation in accordance with said detectedvalues for correctively altering the profile of further delivered strip.

12. A method as defined in claim 11 which includes j. delivering each ofthe transverse profile determinations as a series of thickness-measuringsignals at localities across the strip,

k. said detecting of unwanted profile values comprising converting saidlast-mentioned signals into corresponding signals compared with anaverage thickness characteristic of the preceding profile determinationof the strip, to represent departures from said average thickness, and

1. said adjusting the rolling operations comprising effecting correctivestrip-thickness-altering adjustment at localities across the rolls ofthe rolling operation in accordance with said last-mentionedthickness-departure signals.

13. A method as defined in claim 12 in which in the rolling operationinvolves controlling the shape of the rolls by delivering coolantthereto at localities across the rolls,

n. said corrective strip-thickness-altering adjustment comprisingcontrolling flow of said coolant selectively at said localities forcorrecting unwanted thickness values of the delivered strip profile.

14. Apparatus for measuring the thickness profile across a metal stripmoving lengthwise along a defined path, comprising:

a. a first thickness-measuring means including means for directing athickness-sensitive beam through said path at an angle to the plane of astrip therein, movable to scan such strip with said beam along a lineacross the path of the strip; and

b. a second thickness-measuring means including means for directing asecond thickness-sensitive beam through said path at an angle to theplane of the strip at a selected point substantially on said line; saidbeam-directing means being mutually arranged to direct their respectivebeams at an angleto each other for permitting said firstthicknessmeasuring means in its scanning movement to pass said secondthickness-measuring means at said point without interference ofthickness-measuring functions of said first and second measuring means;said beam-directing means being arranged to direct their beams at acuteangles, to the perpendicular to the plane of the strip, whichrespectively extend in opposite directions of the strip path relative tosaid line.

15. Apparatus as defined in claim 14, which includes means controlled bysaid first and second measuring means and including means for mutuallymodifying the measurements of both said measuring means during scanningmovement of the first measuring means, for producing a measurement ofthe transverse thickness profile of the strip which is unaffected bythickness changes at said point during said scanning movement.

16. Apparatus as defined in claim 15 which includes output meanscontrolled by said last mentioned measurement-producing means, forconverting departures of said measured profile, from desirable profile,into signals representing such departures at successive localitiesacross the strip.

17. Apparatus as defined in claim 16, in combination with adjustablerolling means for producing said strip and means directing the strip inmovement. from the rolling means longitudinally past thethicknessmeasuring means, comprising means controlled by said outputmeans and in response to said signals, for adjusting the rolling meansto correct departures of produced strip from desired profile.

18. Apparatus as defined in claim 14, in which each of thebeam-directing means is arranged to direct its beam at such acute angleof about 15 to about 45.

19. Apparatus as defined in claim 14, in which each of the first andsecond measuring means comprises beam-receiving means and C-shapedsupporting structure, said C-shaped structures being respectivelycomplementary to each other and embracing the path from regions atrespectively opposite edges thereof, each structure carrying the relatedbeam-directing means and beam-receiving means at opposing ends of its Cshape, adjacent to respectively opposite faces of a strip in the strippath.

20. Apparatus as defined in claim 19, which includes means for movingthe supporting structure of the first measuring means crosswise of thepath to effect scanning of the strip with the first beam along saidline.

21. Apparatus as defined in claim 20, which includes means controlled bysaid first and second measuring means and in response to thicknesssignals derived therefrom during travel of the first measuring meansacross the path, and including means modifying the signals from thefirst measuring means by the signals from the second measuring means,for producing a measurement of the thickness profile across the strip.

22. Apparatus as defined in claim 21 which includes output meanscontrolled by said last mentioned measurement-producing means, forconverting departures of said measured profile, from desired flatness,

into a series of signals representative of the existence and extent ofsuch departures at successive localities across the strip. 7

23. Apparatus as defined in claim 21, which is arranged for repeatedoperations, including repeated scanning movements of said firstmeasuring means and resulting thickness profile measurements produced bythe profile-measurement-producing means, and which includes output meanscontrolled by said profile-measurement-producing means and includingmeasurement-storing means, for converting departures of a selectedthickness profile measurement from desired profileas represented by anaveragethickness determined from a preceding profile measurement, intosignals representing such departures at successive localities across thestrip.

24. Apparatus as defined in claim 23, for use in cooperation withadjustable rolling means whereby said strip is delivered in movementpast the first' and second thickness-measuring means, comprisingmeansadapted to control such rolling means for adjustment thereof toalter the profile of the strip delivered from rolling, said rollingadjustment control means being arranged under control'of said outputmeans, foreffecting corrective adjustment in the profile of deliveredstrip.

25. Apparatus as defined in claim 21, in combination with rolling meansfor producing said strip and means directing the strip in movement fromthe rolling means longitudinally past the first 'and secondthicknessmeasuring means,comprising means controlled by said profilemeasurement-producing means for adjusting the rolling means-to correctdepartures of produced strip from desired'flatness of profile. v 26.Apparatus for measuring the thickness profile across a metal stripmoving lengthwise along a defined path, comprising: r

a. two thickness-measuring means each including means directing athickness-sensitive beam through said path at an angle to the plane of astrip therein; b. one of said measuring means being arranged formovement to scan the strip path with ,its beam, along a line across thestrip, and the other measuring means being arrangedfor directing itsbeam at a selected point on said line; c. said angular beam paths of therespective directing means being disposed at a sufficient angle to eachother to permit said moving measuring means to pass said selected pointwithout interference of thickness-measuring functions of said twomeasuring means; each beam being directed at an angle of at least about15 to the perpendicular to the strip plane; and

d. means controlled by said twomeasuring means and in reponse to signalsderived therefrom during scanning of the moving means across the strippath, and including means modifying the signals from the movingmeasuring means by the signals from the other measuring means, forproducing a measurement of the thickness profile across the strip.

27. Apparatus as defined in claim 26, in which each measuring meanscomprises X-ray means facing one surface of the strip for generating anddirecting the angular beam of X-rays and means facing the oppositesurface of the strip for receiving the angular X-ray beam to producesignals responsive to thickness of the.

strip.

28. Apparatus as defined in claim 27, in which each beam is directed atan angle of about 24 to the perpendicular to the strip plane.

29. Apparatus as defined in claim 27, in which each of the two measuringmeans comprises e. C-shaped supporting structure for crosswise embracingthe strip path from opposite edges thereof, having two arms nearrespectively opposite faces of said path, the X-ray means and receivingmeans of said measuring meansbeing respectively disposed in-the arms ofthe corresponding C-shaped structure,

f. the arms of the structure for the scanning measuring means beingdisposed in longitudinal separation along the strip path at selectedopposite sides of the scanning line, and

g. the arms of the structure for the other measuring means beingdisposed in longitudinal separation along the strip path at oppositesides of said line I which are respectively different from the aforesaidselected sides, whereby said other measuring means and itssaid-structure can be disposed to be clear of the scanning movement ofthe scanning measuring means and its said structure.

. 30. Apparatus as defined in claim 29, in-which each of the C-shapedstructures includes for moving it along a predetermined track across thestrip; path, whereby the scanning measuringmeans can be'moved from oneposition clear of the path, inscanning displacements. back and forthacross the path, and whereby. the other tion ,at said point at a centralregion of the path.

31. Apparatus as defined in diam 26, in which each measuring meanscomprises X-ray means facing one surface of the strip for generating anddirecting the angular beam of -rays and means facingthe opposite surfaseof the strip for receiving the angular X-ray beam ,to produce signalsresponsive to thickness of the strip,v

members of each pair being respectively disposed near opposite faces ofa strip in said path and in regions adjacent to opposite sides of a linethat perpendicularly cross the path, in the plane of such strip, saidpairs of members being disposed in mutual complementary relation acrosssaid path, one of said pairs of members being movable crosswise of thepath and the aforesaid dispositions of the supporting members beingmutually arranged to permit the members of the movable pair to movethrough regions unoccupied by the members of the other pair,thickness-measuring means associated with each of said pairs of members,each thicknessmeasuring means including means projecting athickness-sensitive beam between the two members of the pair across saidline in a path at an acute angle to the surface of the strip, saidangles of the beam paths extending oppositely to each other relative tothe path of the strip, whereby the thickness-measuring means carried bythe movable members may scan the width of the strip without interferencewith thickness-measuring operation of the means associated with theother pair of members.

33. Apparatus as defined in claim 32, which includes means controlled bythe respective measuring means of said pairs of members and in responseto thickness signals derived therefrom during travel of the movable pairof members across the width of a strip in the defined path, andincluding means modifying the signals from the movable pair by thesignals from the other pair, for producing a measurement of thethickness profile across the moving strip.

34. Apparatus as defined in claim 32, in which the pairs of members arerespectively provided with mutual supporting elements extending betweenthe upper and lower members of the pairs at regions outside oppositeedges of the strip path, to constitute each of the pairs of members as arigid C-shaped structure with the members respectively extendingcrosswise of the strip path near opposite faces thereof.

Patent No.

Inventor(s) OliVO G. SiVilOtti at 81.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Page 1 of 2 It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column Column insert Column Column 7, line 15, "w'ise" should read wide15, line 57, after "taneous" and before "zone-localized" 18, line 26(Claim 4) "clain" should read claim 18, lines 26 and 27 (Claim 4) after"whereim" delete "beam-generating beam-sensing".

Column 18, line 30 (Claim 4) "eam-generating" should readbeam-generating Column 18, line 58 .(Claim 6) "transversal" should readtraversal Column 20, line 48 (Claim 16) "desirable" should read desired

1. A method of measuring the thickness profile across alengthwise-moving metal strip, comprising: a. scanning the strip along aline transverse of the direction of movement, with a firstthickness-sensitive beam, to provide signals representing thicknessvalues at the successively scanned strip localities; b. simultaneouslythroughout said scanning step measuring the thickness of the movingstrip at a selected stationary point, substantially within said line ofscanning, with a second thickness-sensitive beam to provide signalsrepresenting variations in thickness of the strip at said point duringthe scanning step; c. said beams being mutually disposed and arranged sothat as the first beam scans past said selected point each beam istransmitted through the strip and received, for thicknessmeasuringoperation, without interference with the thicknessmeasuring operation ofthe other beam at said point; the aforesaid disposition of the beamsincluding respectively directing them along paths at sufficient,oppositely extending angles to the perpendicular to the strip surface,to prevent interference of said thickness-measuring operations; and d.combining the signals that result from the first and second beams toprovide a transverse profile determination which is substantiallyunaffected by longitudinal strip thickness variations as represented bythickness variation signals from the selected point.
 2. A method asdefined in claim 1 in which each of said angles is at least about 15*.3. A method as defined in claim 2 in which each of said angles is about24*.
 4. A method as defined in claim 1 wherein: e. said first and secondbeams are transmitted through the strip between corresponding pairs ofbeam-generating and beam-sensing elements respectively near oppositefaces of the strip, f. the elements of the pairs being oppositelystaggered in position lengthwise of the strip, and said beams beingcorrespondingly transmitted at oppositely inclined acute angles to thestrip, g. said scanning step including moving said pair of elements forthe first beam past the said pair of elements for the second beam.
 5. Amethod as defined in claim 1, in cOmbination with producing said movingstrip by rolling operation which is adjustable for altering the profileof the produced strip, said strip being in movement lengthwise from saidrolling operation, which includes h. detecting departure of thetransverse profile of the aforesaid determination from a desiredprofile, and i. adjusting the rolling operation in accordance with saiddetected departure to correct the profile of further production of saidstrip.
 6. In a method of measuring the thickness profile across alength-wise moving metal strip, the steps comprising: a. scanning thestrip along a line perpendicular to the direction of movement, with afirst X-ray beam which traverses the strip at an acute angle to thesurface thereof and which is received after said traversal, to providesignals representing thickness values at the successively scanned striplocalities; and b. simultaneously throughout said scanning stepdirecting to the strip, at a selected point substantially within saidline of scanning, a second X-ray beam which traverses the strip at anacute angle to the surface thereof and which is received after saidtraversal, to provide signals representing variations in thickness ofthe strip at said point during the scanning step; c. the aforesaidtraversal angles of the beams being mutually disposed to provide asufficient angle between beams as the first scans past the second atsaid point to prevent interference between said thickness-sensingoperations with the beams.
 7. A method as defined in claim 6 in whicheach of the beams is directed to the strip at an angle between about 15*and about 45* to the perpendicular to the strip surface, and the anglebetween the beams is at least about 30*.
 8. A method as defined in claim6, which includes combining the signals from the first and second stepsby diminishing the thickness values of the first step signals inaccordance with thickness values of simultaneous second step signals forcancelling the thickness variations at said point from the transversemeasurements to provide a determination of transverse thickness profileof the strip which is substantially independent of longitudinalthickness variations.
 9. A method as defined in claim 8, in which eachof the beams is directed to the strip at an angle between about 15* andabout 30* to the perpendicular to the strip surface, and the anglebetween the beams is at least about 30*.
 10. A method as defined inclaim 9 wherein d. each of said X-ray traversing and signal-providingsteps is effected by projecting the corresponding X-ray beam from afirst element near one face of the strip and receiving and sensing suchbeam at a second element near the opposite face of the strip, e. saidelements for the first beam being separated longitudinally of the stripon selected opposite sides of said scanning line, said scanningoperation being effected by moving said elements for the first beamtogether across the path of the strip, and f. said elements for thesecond beam being separated longitudinally of the strip on oppositesides of the scanning line which are respectively different from theaforesaid selected sides, whereby said second beam elements are disposedclear of the scanning movement of the first beam elements.
 11. A methodas defined in claim 8, in combination with producing said moving stripby rolling operation which is adjustable for altering the profile of theproduced strip, said moving strip being in its aforesaid longitudinalmovement as delivered under tension from said rolling operation, whichincludes g. making successive determinations of transverse thicknessprofile along a continuous strip by the aforesaid steps, h. detectingunwanted thickness values in such profile in said successivedeterminations, and i. adjusting the rolling operation in accordancewith said detected values for correctively altering The profile offurther delivered strip.
 12. A method as defined in claim 11 whichincludes j. delivering each of the transverse profile determinations asa series of thickness-measuring signals at localities across the strip,k. said detection of unwanted profile values comprising converting saidlast-mentioned signals into corresponding signals compared with anaverage thickness characteristic of the preceding profile determinationof the strip, to represent departures from said average thickness, and13. A method as defined in claim 12 in which m. the rolling operationinvolves controlling the shape of the rolls by delivering coolantthereto at localities across the rolls, n. said correctivestrip-thickness-altering adjustment comprising controlling flow of saidcoolant selectively at said localities for correcting unwanted thicknessvalues of the delivered strip profile.
 14. Apparatus for measuring thethickness profile across a metal strip moving lengthwise along a definedpath, comprising: a. a first thickness-measuring means including meansfor directing a thickness-sensitive beam through said path at an angleto the plane of a strip therein, movable to scan such strip with saidbeam along a line across the path of the strip; and b. a secondthickness-measuring means including means for directing a secondthickness-sensitive beam through said path at an angle to the plane ofthe strip at a selected point substantially on said line; c. saidbeam-directing means being mutually arranged to direct their respectivebeams at an angle to each other for permitting said firstthickness-measuring means in its scanning movement to pass said secondthickness-measuring means at said point without interference ofthickness-measuring functions of said first and second measuring means;said beam-directing means being arranged to direct their beams at acuteangles, to the perpendicular to the plane of the strip, whichrespectively extend in opposite directions of the strip path relative tosaid line.
 15. Apparatus as defined in claim 14, which includes meanscontrolled by said first and second measuring means and including meansfor mutually modifying the measurements of both said measuring meansduring scanning movement of the first measuring means, for producing ameasurement of the transverse thickness profile of the strip which isunaffected by thickness changes at said point during said scanningmovement.
 16. Apparatus as defined in claim 15 which includes outputmeans controlled by said last mentioned measurement-producing means, forconverting departures of said measured profile, from desired profile,into signals representing such departures at successive localitiesacross the strip.
 17. Apparatus as defined in claim 16, in combinationwith adjustable rolling means for producing said strip and meansdirecting the strip in movement from the rolling means longitudinallypast the thickness-measuring means, comprising means controlled by saidoutput means and in response to said signals, for adjusting the rollingmeans to correct departures of produced strip from desired profile. 18.Apparatus as defined in claim 14, in which each of the beam-directingmeans is arranged to direct its beam at such acute angle of about 15* toabout 45*.
 19. Apparatus as defined in claim 14, in which each of thefirst and second measuring means comprises beam-receiving means andC-shaped supporting structure, said C-shaped structures beingrespectively complementary to each other and embracing the path fromregions at respectively opposite edges thereof, each structure carryingthe related beam-directing means and beam-receiving means at opposingends of its C shape, adjAcent to respectively opposite faces of a stripin the strip path.
 20. Apparatus as defined in claim 19, which includesmeans for moving the supporting structure of the first measuring meanscrosswise of the path to effect scanning of the strip with the firstbeam along said line.
 21. Apparatus as defined in claim 20, whichincludes means controlled by said first and second measuring means andin response to thickness signals derived therefrom during travel of thefirst measuring means across the path, and including means modifying thesignals from the first measuring means by the signals from the secondmeasuring means, for producing a measurement of the thickness profileacross the strip.
 22. Apparatus as defined in claim 21 which includesoutput means controlled by said last mentioned measurement-producingmeans, for converting departures of said measured profile, from desiredflatness, into a series of signals representative of the existence andextent of such departures at successive localities across the strip. 23.Apparatus as defined in claim 21, which is arranged for repeatedoperations, including repeated scanning movements of said firstmeasuring means and resulting thickness profile measurements produced bythe profile-measurement-producing means, and which includes output meanscontrolled by said profile-measurement-producing means and includingmeasurement-storing means, for converting departures of a selectedthickness profile measurement from desired profile as represented by anaverage thickness determined from a preceding profile measurement, intosignals representing such departures at successive localities across thestrip.
 24. Apparatus as defined in claim 23, for use in cooperation withadjustable rolling means whereby said strip is delivered in movementpast the first and second thickness-measuring means, comprising meansadapted to control such rolling means for adjustment thereof to alterthe profile of the strip delivered from rolling, said rolling adjustmentcontrol means being arranged under control of said output means, foreffecting corrective adjustment in the profile of delivered strip. 25.Apparatus as defined in claim 21, in combination with rolling means forproducing said strip and means directing the strip in movement from therolling means longitudinally past the first and secondthickness-measuring means, comprising means controlled by saidprofile-measurement-producing means for adjusting the rolling means tocorrect departures of produced strip from desired flatness of profile.26. Apparatus for measuring the thickness profile across a metal stripmoving lengthwise along a defined path, comprising: a. twothickness-measuring means each including means directing athickness-sensitive beam through said path at an angle to the plane of astrip therein; b. one of said measuring means being arranged formovement to scan the strip path with its beam, along a line across thestrip, and the other measuring means being arranged for directing itsbeam at a selected point on said line; c. said angular beam paths of therespective directing means being disposed at a sufficient angle to eachother to permit said moving measuring means to pass said selected pointwithout interference of thickness-measuring functions of said twomeasuring means; each beam being directed at an angle of at least about15* to the perpendicular to the strip plane; and d. means controlled bysaid two measuring means and in response to signals derived therefromduring scanning of the moving means across the strip path, and includingmeans modifying the signals from the moving measuring means by thesignals from the other measuring means, for producing a measurement ofthe thickness profile across the strip.
 27. Apparatus as defined inclaim 26, in which each measuring means comprises X-ray means facing onesurface of the strip for generating and directing the angular beam ofX-rays and means facing the oppoSite surface of the strip for receivingthe angular X-ray beam to produce signals responsive to thickness of thestrip.
 28. Apparatus as defined in claim 27, in which each beam isdirected at an angle of about 24* to the perpendicular to the stripplane.
 29. Apparatus as defined in claim 27, in which each of the twomeasuring means comprises e. C-shaped supporting structure for crosswiseembracing the strip path from opposite edges thereof, having two armsnear respectively opposite faces of said path, the X-ray means andreceiving means of said measuring means being respectively disposed inthe arms of the corresponding C-shaped structure, f. the arms of thestructure for the scanning measuring means being disposed inlongitudinal separation along the strip path at selected opposite sidesof the scanning line, and g. the arms of the structure for the othermeasuring means being disposed in longitudinal separation along thestrip path at opposite sides of said line which are respectivelydifferent from the aforesaid selected sides, whereby said othermeasuring means and its said structure can be disposed to be clear ofthe scanning movement of the scanning measuring means and its saidstructure.
 30. Apparatus as defined in claim 29, in which each of theC-shaped structures includes for moving it along a predetermined trackacross the strip path, whereby the scanning measuring means can be movedfrom one position clear of the path, in scanning displacements back andforth across the path, and whereby the other measuring means can bemoved from an opposite position clear of the path to a position formeasuring function at said point at a central region of the path. 31.Apparatus as defined in claim 26, in which each measuring meanscomprises X-ray means facing one surface of the strip for generating anddirecting the angular beam of X-rays and means facing the oppositesurface of the strip for receiving the angular X-ray beam to producesignals responsive to thickness of the strip, and in which said signalmodifying means comprises a difference circuit wherein thickness valuesof the scanned signals are reduced by thickness values of the signalsfrom the selected point, to yield signals representing thickness profilevalues across the strip corresponding to constant thickness at saidpoint.
 32. Apparatus for measuring the thickness profile across a metalstrip moving lengthwise along a defined path, comprising two pairs ofsupporting members, the members of each pair being respectively disposednear opposite faces of a strip in said path and in regions adjacent toopposite sides of a line that perpendicularly crosses the path, in theplane of such strip, said pairs of members being disposed in mutualcomplementary relation across said path, one of said pairs of membersbeing movable crosswise of the path and the aforesaid dispositions ofthe supporting members being mutually arranged to permit the members ofthe movable pair to move through regions unoccupied by the members ofthe other pair, thickness-measuring means associated with each of saidpairs of members, each thickness-measuring means including meansprojecting a thickness-sensitive beam between the two members of thepair across said line in a path at an acute angle to the surface of thestrip, said angles of the beam paths extending oppositely to each otherrelative to the path of the strip, whereby the thickness-measuring meanscarried by the movable members may scan the width of the strip withoutinterference with thickness-measuring operation of the means associatedwith the other pair of members.
 33. Apparatus as defined in claim 32,which includes means controlled by the respective measuring means ofsaid pairs of members and in response to thickness signals derivedtherefrom during travel of the movable pair of members across the widthof a strip in the defined path, and including means modifying thesignals from the movable pair by the signalS from the other pair, forproducing a measurement of the thickness profile across the movingstrip.
 34. Apparatus as defined in claim 32, in which the pairs ofmembers are respectively provided with mutual supporting elementsextending between the upper and lower members of the pairs at regionsoutside opposite edges of the strip path, to constitute each of thepairs of members as a rigid C-shaped structure with the membersrespectively extending crosswise of the strip path near opposite facesthereof.